ABSTRACT
Bis(diimine)-ruthenium complexes constitute a class of catalysts with good activity for oxidation reactions, such as sulfoxidation and epoxidation. The synthesis and the full characterization of a new ruthenium complex bearing an original pentadentate ligand (L5pyr for 2,6-bis-(6-ethyl-2,2'-bipyridyl)-pyridine) is reported. Comparison of its activity with regard to[Ru(bpy)2(CH3CN)2](2+) and [Ru(bpy)2(py)(CH3CN)](2+) during alkene and sulfide oxidation allowed us to conclude that the addition of a fifth pyridine ligand in the coordination sphere improves the efficiency of the catalyst. Moreover, under these oxidation conditions a hydroxylation of the ligand L5pyr led to a better activity than its analogue [Ru(bpy)2(py)(CH3CN)](2+), especially during epoxidation of alkenes by PhI(OAc)2.
ABSTRACT
cis-[Ru(dmp)(2)(CH(3)CN)(2)][PF(6)](2) (dmp = 2,9-dimethyl-1,10-phenanthroline), complex 1[PF(6)](2), exists in two enantiomeric forms, Delta and Lambda. During treatment with the chiral anion tris[tetrachlorobenzene-1,2-bis(olato)]phosphate(V), also named Trisphat, in dichloromethane it has been possible to selectively precipitate each enantiomer, associated with Trisphat in the form of the heterochiral pair. This enantiomerically pure compound has been characterized in solution by UV-visible, CD, ESI-MS, and NMR spectroscopy and by X-ray crystallography in the solid state. Trisphat was also used as an NMR chiral shift reagent to determine the enantiomeric excess of the complex preparations. The "chiral-at-metal" ruthenium complex has been evaluated as a catalyst for the oxidation of sulfides to sulfoxides by hydrogen peroxide. The reactions displayed a low but significant level of enantioselectivity (18% ee in the case of 4-bromophenyl methyl sulfide). Our results thus provide the first demonstration that the chiral information carried by a stereogenic metal center can be catalytically transferred to molecules during stereoselective oxidation.
